I had a 2G iPhone jb for t-mobile and just upgraded to iPhone 4 but switched to AT&T. After my first sync, the carrier name in the status bar switched to saying "T-Mobile" even though it's not a jb phone! Anyone know how to fix this so it displays the correct carrier name ("AT&T")?

Lol did you somehow tweak your carrier name (like use "MakeItMine" from cydia) to display T-mobile? I'm guessing it's got something to do with restoring from backup.

A solution would be to sync all your contacts, songs, apps, etc. with iTunes and then restore and set up as a new phone. I didn't restore from backup because the phone tends to operate faster when set up as a new phone. I did the same thing you did (switch to AT&T) yesterday and didn't experience this issue at all.

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Yea the most important part is syncing your contacts. Make sure they sync from your iPhone TO your computer, that way they'll carry over. You can use outlook contacts or windows contacts. Also, any internal app data will be lost (ie. bank account info, saved games, etc). iTunes will save your apps but not it's individual data. Also, sync your pictures or save them from the DCIM folder in "My computer - iPhone"

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Lol it's gotta be your old settings. You might just have to wait until the phone is jailbroken, when that happens you'll be able to change it. Hey on the bright side, you might be able to spook a bunch of people by telling them you're using T-mobile in a un-jailbroken iPhone 4 with 3G speeds...

Or you can take it to an Apple store and punk a Genius. Lol I'm just throwing out ideas sorry...I just think it's hilarous that you have T-mobile in your carrier in an un-jailbroken phone.

One last thing I'd try is going into reset - reset settings (not the one that says all settings & data). but this will clear out any settings and you will have to re-enter (ie. e-mail accounts, etc.)

It looks like several JB files (e.g., springboard and other JB apps) remained in the backup (which makes sense - it's how apps like AptBackup work) and transfer to my UNmodded iPhone 4. Anyway, I edited the SBFakeCarrier name to AT&T (oh, the irony) using the program in that link, restored, and viola! :-)